Biology
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p14a..04r&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P14A-04
Biology
[1055] Geochemistry / Organic And Biogenic Geochemistry, [5200] Planetary Sciences: Astrobiology, [6040] Planetary Sciences: Comets And Small Bodies / Origin And Evolution, [6240] Planetary Sciences: Solar System Objects / Meteorites And Tektites
Scientific paper
Chondrites accreted primitive components, including organic compounds sampled from the proto-solar nebula. However, the molecular and isotopic fingerprints of organic matter extracted from chondrites are also potentially influenced by complex evolution on the parent bodies. We have performed NanoSIMS in situ characterisation of organic matter in the matrices of carbonaceous chondrites Orgueil (CI), Murchison (CM), Tagish Lake (C2), Renazzo (CR) and Allende (CV) with a spatial resolution of ~200 nm; we could also constrains textural relationships between organic constituents and other phases. Those meteorites have undergone a diverse set of parent body processes. I.e., CI, C2 and CM meteorites have undergone aqueous alteration, and the CV’s are thermally metamorphosed. The CR’s are inferred to be the least altered class of chondrites. Despite these differences in parent body modification, the distributions of organic carbon in these meteorites is similar: in all cases it can be found as micron-size, randomly distributed organic particles that are surrounded by the clay minerals that dominate the matrix material, but are not specifically associated with sulfides, sulfates or oxides. In addition, there is a “diffuse” fraction of organic carbon intimately associated with the clay-rich matrix. We hypothesize that the C particles we identify are hosts of insoluble organic matter that co-accreted with other primitive constituents of these materials, whereas the diffuse C fraction is the soluble component (i.e., soluble in laboratory organic and aqueous solvents). Our analytical technique lacks the spatial resolution required to analyze the diffuse organic matter without contamination by associated clays. But we are able to analyze the compositions of the interiors of relatively large C-rich particles (>500 nm) without such contamination. Some fraction of the C-rich particles in all of the examined meteorites but Allende exhibit a very high enrichment in deuterium (up to 20000 ‰); that is, some such particles are D-rich ‘hot spots’ previously recognized in separates of IOM from CI, CM and CR meteorites (see Busemann et al, Science 2006). The spatial variation of D/H ratios across D-rich carbon particles shows no evidence for H-isotope exchange with adjacent D-poor clays, even in the samples that have undergone the greatest extents of aqueous alteration. Moreover, chemical and isotopic compositions of these particles differ from one another across ~100 µm length scales in the same meteorite. And, the range of compositions of organic particles for different meteorites overlap one another (that is, they appear to all sample a similar population of C-rich particles). We hypothesize that nebular processes (including large scale particle motion, UV-irradiation of low temperature areas and high temperature reactions) generated a heterogeneous population of C-rich particles, some of which were D-rich. This mixed population was sampled by chondritic parent bodies during their accretion and the isotopic and chemical compositions remained relatively unchanged during parent body alteration.
Eiler John M.
Guan Yifeng
Remusat Laurent
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